How would you do that in an actually useful way though?
Giving a player a grade is meaningless if they can't see why they got that grade what it's comprised of. or how to improve it.
If a player does expert today and gets rank a but tomorrow only gets a rank c despite thinking he's played the same. He needs to be able to see what changed. And there is no simple or obvious way to do that.
Today that player might be doing most of the damage because the other dps is playing badly thus he gets an A rank. Tomorrow he might play exactly the same but do proportionately less damage because the other dps is making a bigger contribution so only gets a C rank..
You need details. There are so many variables some many of which aren't too obvious or even quantifiable easily but they can have a significant effect. If you don't have details players will see major fluctuations in There grades and be unable to quantify why. And If they can't quantify why. The system is useless. May as well just be rng. Roll a dice Today you get a b..
I generally think this is why yoshi never implements them because its simply impossible to make it accurate or even useful.
Even ACT isn't accurate. Back doing Susan ex for example I could have some major variance in my dps. And act wouldn't know why. It might pick up a lower uptime but it wouldn't be able to quantify why that was. Was I being lazy. Was I jailed by rocks every time or targeted for lightning. Was Susan tanked in a stupid place...
Don't really have more recent examples as I've fallen behind on content and tired of the treadmill